1. Field of the Invention
The present invention relates to a multiple fiber optical cable in which plural optical fibers are bundled, and to a method of manufacturing the multiple fiber optical cable. The term xe2x80x9ccablexe2x80x9d to be used in this application encompasses an optical fiber ribbon.
2. Related Back Ground Art
Optical fibers in their longitudinal direction of which the light propagation characteristic changes in order to improve the light propagation characteristic of optical fiber transmission lines in optical communication systems have been known. For example, an optical fiber disclosed in Japanese Patent Application Laid-Open No. HEI 8-320419 is one in which the core diameter or the refractive index of core is changed in the longitudinal direction of the optical fiber, so as to adjust chromatic dispersion, and in which positive dispersion section and negative dispersion section having positive dispersion and negative one, respectively, are disposed alternately. The optical fiber disclosed in Japanese Patent Application Laid-Open No. HEI 11-30725 is one in which the core diameter and the fiber diameter are changed in the longitudinal direction so as to adjust chromatic dispersion, and in which positive dispersion section and negative dispersion section having positive dispersion and negative one, respectively, are disposed alternately. The respective optical fibers disclosed in these two publications lower the absolute value of average chromatic dispersion as a whole, while enhancing the absolute value of chromatic dispersion in each of the positive dispersion section and negative dispersion section, thereby making it possible to prevent transmission quality deterioration being due to nonlinear optical phenomena or cumulative chromatic dispersion.
On the other hand, the optical fiber disclosed in Japanese Patent Application Laid-Open No. HEI 10-139463 is one in which the drawing tension upon drawing is alternately changed between a higher tension value and a lower tension value so as to adjust the residual stress, according to which chromatic dispersion is changed in the longitudinal direction. As a consequence, the loss resulting from Brillouin scattering can be reduced. The optical fiber disclosed in Japanese Patent Application Laid-Open No. HEI 10-167750 is one in which the drawing tension at the time of drawing is changed so as to adjust the residual stress, according to which chromatic dispersion is changed in the longitudinal direction. As a consequence, soliton pulse compression can be effected.
In addition, there are cases where plural optical fibers are bundled into a multiple fiber optical cable in order to increase the capacity of optical communication. The term xe2x80x9cmultiple fiber optical cablexe2x80x9d to be used herein encompasses an optical fiber cable in which plural optical fibers are bundled, a tape-shaped ribbon in which plural optical fibers are arranged in parallel in a flat shape and are integrally coated, an optical fiber cable in which plural such ribbons are bundled, or the like. The term xe2x80x9coptical cablexe2x80x9d is used as the term xe2x80x9cmultiple fiber optical cablexe2x80x9d hereinbelow.
In order to improve the optical propagation characteristics of optical fiber transmission paths in optical communication systems and to increase the capacity of optical communication, it can be considered to use an optical cable formed by preparing plural optical fibers each of which has a chromatic dispersion characteristic changed in its longitudinal direction, and bundling these plural optical fibers into an optical cable. However, the inventor of the present application has found out that such an optical cable has the following problems.
Specifically, since the optical propagation characteristic of each of the optical fibers of the optical cable changes in its longitudinal direction, if the optical cable is cut into a predetermined length, the overall optical propagation characteristic of the optical cable may differ from a desired value even if the overall optical propagation characteristic of each of the bundled plural optical fibers has a desired value. In addition, when an optical fiber ribbon is connected or spliced to other optical fibers, the resultant overall optical propagation characteristic inclusive of that of the other optical fibers may differ from a desired value. Furthermore, each of the plural optical fibers bundled in the optical fiber ribbon will show a different change in its overall optical propagation characteristic.
In an optical fiber ribbon in which diameter of each of plural optical fibers is changed to adjust the optical propagation characteristic thereof, the losses of fusion splicing to other optical fibers may become large depending on the diameter of each fiber at each end of the ribbon. In addition, in this cases when the optical fiber ribbon is to be connected to other optical fibers by means of an optical fiber connector, if the fiber diameter of each of the optical fibers bundled in the optical fiber ribbon is larger than a diameter of a ferrule of the optical fiber connector, the optical fiber cannot be inserted into the ferrule. On the other hand, if the fiber diameter of each of the optical fibers bundled in the optical fiber ribbon is smaller than the diameter of the ferrule of the optical fiber connector, the central position of the optical fiber in the ferrule is not defined, so that connection losses or splice losses may become large.
The present invention has been made to solve the above-described problems, and the purpose is to provides an optical cable which Includes bundled plural optical fibers of which is changed optical propagation characteristic in their respective longitudinal directions so that degradations or deviations can be restrained from occurring in the chromatic dispersion characteristics during cutting or connection.
The optical cable according to the present invention is characterized plural optical fibers which have chromatic dispersion characteristics changing in their respective longitudinal directions are bundled so that the chromatic dispersion characteristics of the respective plural optical fibers coincide with each other at the end positions at least.
According to this optical cable, since the chromatic dispersion characteristics of the respective plural optical fibers coincide with each other at the end positions, the overall chromatic dispersion characteristic of each of the optical fibers which constitute the optical cable can be made to have a desired value. Since the chromatic dispersion characteristics of the respective plural optical fibers coincide with each other at the end positions in this manner, even if other optical fibers are connected or spliced to the respective plural optical fibers, the amounts of changes due to the connection or splice in the overall optical propagation characteristics inclusive of those of the respective plural optical fibers and those of the other optical fibers remain the same if the other optical fibers have the same characteristics. Accordingly, in this optical cable, if the initial overall chromatic dispersion characteristics of the respective plural optical fibers are the same, when the respective plural optical fibers are connected or spliced to the other optical fibers, the resultant overall chromatic dispersion characteristics remain the same, whereby the overall chromatic dispersion characteristics of the respective optical fibers can readily be made to have desired values and degradations and deviations in chromatic dispersion characteristic due to the connection or splice can be restrained. In addition, the optical cable can be cut so that the chromatic dispersion characteristics of the respective optical fibers are the same from one end of the optical cable to a cut portion. In particular, in the case where the chromatic dispersion characteristics of the respective optical fibers coincide with each other at individual locations in the longitudinal direction, even if the optical cable is partly cut at one end, the amounts of changes due to this cutting in the chromatic dispersion characteristics of the respective plural optical fibers are the same.
The optical cable in accordance with the present invention may be characterized in that each of the bundled plural optical fibers is provided with identification marks for identifying chromatic dispersion characteristics at its individual locations in the longitudinal direction. In this case, on the basis of these identification marks, it is possible to identify the chromatic dispersion characteristics of each of the plural optical fibers at the individual locations in the longitudinal direction thereof. Accordingly, it is possible to confirm the chromatic dispersion characteristic of each of the plural optical fibers at the end position during cutting or connecting or splicing.
The optical cable in accordance with the present invention may be characterized in that the chromatic dispersion characteristics of the respective bundled plural optical fibers coincide with each other at individual locations in the longitudinal direction of the optical cable, and a surrounding member of the plural optical fibers is provided with an identification mark for identifying the chromatic dispersion characteristics at the individual locations in the longitudinal direction. In this case, on the basis of the identification mark provided on the surrounding member of the plural optical fibers, it is possible to identify the chromatic dispersion characteristics of each of the plural optical fibers at its individual location in the longitudinal direction. Accordingly, it is possible to confirm the chromatic dispersion characteristic of each of the plural optical fibers at the end position during cutting or connecting or splicing.
An optical cable manufacturing method according to the present invention includes the steps of: producing plural optical fibers which have changing chromatic dispersion characteristics and which are provided with identification marks for identifying the each of their chromatic dispersion characteristics at their individual locations in the longitudinal direction; and the optical cable is produced by bundling the plural optical fibers on the basis of the identification marks provided on the respective plural optical fibers so that the chromatic dispersion characteristics of the respective optical fibers coincide with each other at at least the end position of the optical cable.
Another optical cable manufacturing method according to the present invention includes the steps of: producing plural optical fibers which have chromatic dispersion characteristics changing in their respective directions in the longitudinal direction, the chromatic dispersion characteristics of each of the plural optical fibers at individual locations in the longitudinal direction thereof being memorized when each of the plural optical fibers is being produced; and the optical cable is produced by bundling the plural optical fibers, on the basis of the chromatic dispersion characteristics at the individual locations in the longitudinal direction which are memorized to each of the plural optical fibers, so that the chromatic dispersion characteristics of the respective optical fibers coincide with each other at at the least end position of the optical cable.
According to either of these optical cable manufacturing methods, it is possible to suitably manufacture the optical cable according to the present invention.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.